From The Earth Is Weeping: The Epic Story of the Indian Wars for the American West, by Peter Cozzens (Knopf, 2016), Kindle Loc. 1154-1167:
Even as the Indian Wars intensified, Congress—intent on paying down the massive national debt incurred during the Civil War—repeatedly reduced the rolls of the regular army. From an authorized strength of fifty-four thousand men in 1869, the army would plummet to just twenty-five thousand by 1874. Reconstruction duties siphoned off a third of the army and sucked the institution into partisan politics. As Southern states were readmitted to the Union, their representatives made common cause with the budget balancers in order to emasculate their blue-coated former oppressors, and the frontier army became a skeleton force.
Declining numbers were not the army’s only problem. Gone were the sober and purposeful volunteers who had restored the Union. In their place was a decidedly inferior brand of soldier. Not all were “bummers and loafers,” as the New York Sun alleged. There were also a disproportionately large number of urban poor, criminals, drunkards, and perverts. Few soldiers were well educated, and many were illiterate. Unskilled laborers in search of a steady job flocked to recruiting depots, usually to desert when better-paying work became available. One-third of the frontier army consisted of recent immigrants, mostly German and Irish, some of whom had seen service in European armies and proved an asset, and sprinkled among the American undesirables were good men who had fallen on hard times. Nevertheless, as one general observed, while the army had a greatly improved rifle, “I rather think we have a much less intelligent soldier to use it.”
Incentives to enlist were few. By the 1870s, regulars earned just ten dollars a month, three dollars less than had Civil War volunteers a decade earlier.